/* 
  enter的两个是进入时的两个形态变化
  leave的两个是离开时的两个形态变化
  .页面过渡指令的name属性-enter-active
  .页面过渡指令的name属性-leave-active
  .页面过渡指令的name属性-enter
  .页面过渡指令的name属性-leave-to
*/
.modify-enter-active,
.modify-leave-active {
  transition: opacity 2s;
}
.modify-enter,
.modify-leave-to {
  opacity: 0;
}
